Conventionally, a construction machine has been proposed that has an electric motor as a power source for a rotation mechanism for rotating an upper-part rotating body. In such a construction machine, the rotation mechanism is accelerated (driven) by the power running operation of the electric motor, while a regenerative operation is performed at the time of decelerating (braking) the rotation mechanism to charge a battery with generated electric power (for example, Patent Document 1). Further, the construction machine described in Patent Document 1 has a hydraulic pump in order to hydraulically drive other drive mechanisms than the rotation mechanism, and has a generator connected via a speed-increasing machine to an engine for driving this hydraulic pump, so as to use the electric power produced by power generation to charge the battery and to drive the electric motor of the rotation mechanism.
[Patent Document 1] Japanese Laid-Open Patent Application No. 2004-036303